1. Field of the Invention
The present invention relates to a honeycomb structure.
2. Description of the Related Art
A large number of techniques have been developed in relation to conversion of automobile exhaust gas. With an increase in traffic, however, countermeasures taken against exhaust gas have hardly been satisfactory. Not only in Japan but also globally, is automobile emission control going to be further tightened.
In order to meet such control, a catalyst support capable of treating predetermined components contained in exhaust gas is used in exhaust gas systems. Further, a honeycomb structure is known as a member for such a catalyst support.
This honeycomb structure has, for example, multiple cells (through holes) extending from one to another of the end faces of the honeycomb structure along its longitudinal directions, and these cells are separated from each other by cell walls supporting a catalyst. Accordingly, in the case of causing exhaust gas to flow through this honeycomb structure, substances contained in the exhaust gas, such as HC (a hydrocarbon compound), CO (carbon monoxide), and NOx (nitrogen oxides), are converted (oxidized or reduced) by the catalyst supported by the cell walls, so that these components in the exhaust gas may be treated.
In general, the cell walls (base material) of such a honeycomb structure are formed of cordierite. Further, a catalyst support layer of γ-alumina is formed on the cell walls, and a catalyst of a noble metal such as platinum and/or rhodium is supported on this catalyst support layer.
Further, a technique has been proposed that, in order to improve conversion performance at exhaust gas temperatures lower than a temperature at which a catalyst becomes active, uses a honeycomb structure of a relatively low resistance and supplies the honeycomb structure with electric current via electrodes for voltage application provided on the honeycomb structure, thereby causing the honeycomb structure to perform self-heating (Japanese Laid-Open Utility Model Application No. 49-124412).
The entire contents of Japanese Laid-Open Utility Model Application No. 49-124412 are incorporated herein by reference.